Implied Probability

The Short Version

Odds and probabilities are the same thing written two different ways. When a sportsbook posts -150on a team, it is really saying “we think this team wins about 60% of the time.” Implied probability is just that hidden percentage, pulled back out of the price. Learn the conversion and every odds board turns into a list of win probabilities you can compare against your own.

Converting American Odds

American odds come in two flavors, so there are two formulas. The minus sign marks the favorite; the plus sign marks the underdog.

Negative odds (favorites):

implied % = (odds) / (odds + 100) × 100

For -150, that is 150 / (150 + 100) = 150 / 250 = 60%. For -200, it is 200 / 300 = 66.7%.

Positive odds (underdogs):

implied % = 100 / (odds + 100) × 100

For +130, that is 100 / (130 + 100) = 100 / 230 = 43.5%. For +250, it is 100 / 350 = 28.6%.

Converting Decimal and Fractional Odds

Outside the US, odds usually come as decimals, and the math is far simpler — implied probability is just the reciprocal:

implied % = (1 / decimal odds) × 100

Decimal 2.50 is 1 / 2.50 = 40%. Decimal 1.67 is 1 / 1.67 ≈ 60%. Fractional odds work the same way once you turn them into a decimal: 6/4 means 6 ÷ 4 = 1.5 profit per unit, or a decimal price of 2.50, which is again 40%.

The Catch: The Vig

Add up both sides of a real market and you will get more than 100%. Take a classic -110 / -110 line: each side implies 110 / 210 = 52.4%, and 52.4% + 52.4% = 104.8%. Probabilities cannot really sum to 104.8% — that extra 4.8% is the vig(also called the juice, margin, or overround): the sportsbook's commission, baked straight into the price.

This is why the raw implied probability always overstatesthe book's true belief. Each side is padded so the house profits no matter which team wins.

Removing the Vig

To recover the book's genuine estimate, divide each side's implied probability by the total of both sides. That normalizes them back to 100%:

true % = side implied % / (both sides added together)

For the -110 / -110 market: 52.4% / 104.8% = 50.0% per side — an honest coin flip, once the commission is stripped out. For a lopsided line like -200 (66.7%) against +170 (37.0%), the total is 103.7%, so the vig-free favorite is 66.7% / 103.7% ≈ 64.3%. That devigged number is the one worth comparing against a model.

Turning It Into an Edge

Implied probability is the bridge that lets you compare a price to an opinion. Convert the odds, remove the vig, and you have the market's honest estimate in plain percentage terms. Now line it up against an independent number:

• If your estimate is higher than the vig-free market, the odds are paying more than the risk deserves — a potential value bet.
• If your estimate is lower, the market is more confident than you are, and the price is not worth it.
• If they match, the market has already priced in what you know.

That comparison is exactly what our value betssurface: our model's win probability set against the vig-free market price, so the gap is visible without doing the arithmetic yourself. To understand what those percentages mean in the first place, start with how to read a win probability, and see how we build ours on the methodology page.

The Bottom Line

Every set of odds is a win probability in a costume. Convert it (odds to percentage), undress it (remove the vig), and compare it (against your own number). Do that and you stop reading a betting board as prices and start reading it as probabilities — which is the only way to tell when one is wrong.